Brussels sprout picking robot: an insightful first year

Henk-Willem Molenaar, director of Tumoba, points to the four-row sprout picker a hundred yards away. “That one is standing still, because the pickers are having a break to eat.” What he means to say is that rest breaks are not an issue for the fully automated picker. The ASH-4, as Tumoba’s picking robot is officially referred to, is at work on the same plot as the manned Tumoba harvester.

It is mid-December, both machines are harvesting Brussels sprouts for growers Ronald and Jan Herbert in Zeewolde. The brothers own the robot picker, and also provided the necessary input during development. This included the positioning of the cabin, and the addition of an extra picking head on the side for – if necessary – manual input of Brussels sprout plants. According to them, it is unlikely picking sprouts can be fully robotised in the short term. “The crop has to be suitable for it. At the moment, conventional pickers are still needed.”

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Automated picking in practice

The ASH-4 picking robot (Automatic Sprout Harvester, four-row) was put into operation at the end of last season. At the time, this gave a brief opportunity to see how automated picking would work out in practice, with the possibility of making technical adjustments during the past summer months.

Of course it would be nice if the picking robot would run smoothly from the first meters. But that was wishful thinking, given the nature of the product to be harvested and because of all the actions required to guide a sprout plant from its growing spot to the picking head fully automatically, without manual intervention or adjustment.

The picking principle just works, that’s for sure

Just under a year later and having gained the necessary experience, the robot is well on its way to the operational reliability you can demand from this sprout picker, Molenaar says. “The picking principle just works, that’s for sure. Up to now, we have also been able to solve technical imperfections. Which does not alter the fact that some events did surprise us: think of parts that did not hold up because they always make the same movement. Or the effects of vibration and shock movements that a picker always makes. When developing a machine you always try to take this into account, but once in practice things can turn out differently than expected.”

The rear part of the ASH-4 – from the picking heads on – is similar to a conventional four-row harvester, including a 10-ton storage bunker and a pre-reading unit for initial quality sorting in the field. The difference is in the front part of the picker, where the four robots for trimming, positioning and feeding the plants into the picker head hang. This makes the ASH-4 more robust and longer.

Larger track undercarriage

That’s why, compared to a conventional picker, a larger track undercarriage was chosen for a ground pressure of up to 0.5 kg/cm2, and an engine capable of delivering 320 hp instead of 120 hp. That extra power is partly needed to drive the picking robots. This is done hydraulically, which is the most practical from a technical point of view and because of the operational reliability under the wet/winter conditions under which the picker has to do its work.

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600 to 720 stems per hour

The net capacity of each individual robot is 600 to 720 stems per hour, which is comparable to manual harvesting. Each action – such as cutting off the sprouts, removing the trunk and dropping the leaf – takes a certain amount of time. This requires a certain driving speed, not unlike that on a hand picker, always depending on how the crops are planted and on the harvesting conditions.

A conventional harvester uses a saw to harvest the plant. The disadvantage of sawing is that it is impossible to determine exactly when the stem has been completely cut. The robot however cuts the stem. Moreover, the cutting is done very close to the ground. “The plants are arranged in a straight row just above the ground and at a fixed distance from each other,” Molenaar explains. “Higher above the ground, a straight planting row is in reality not that straight. For manual picking, that doesn’t matter much. In automatic harvesting, the plants should be in a straight line as much as possible.”

Because of the precision required, each plant is positioned – as far as necessary – upright. That positioning is done prior to cutting. This process is controlled with switches, no cameras are used because of reliability, says Molenaar. “Leaves may be in front of the camera lens for instance. Cameras are only mounted for surveillance.”

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Operator is required

However, when plants are very crooked or thickened, the positioning system is not always able to line them up as desired. If, as a result, things go wrong when maneuvering a plant in front of the picking head or when feeding it into the picking head, the safety system intervenes: the picker stops. Before restarting, the problem must first be solved (if intervention is required at all).

This means an operator is required at all times, to ensure the machine can continue picking.The operator also takes care of the re-routing and positioning of the machine between jobs. This can be done from the cabin, or from the outside with a radio-controlled system.